Electrically switchable liquid crystal-polymer films intended for use in various electro-optical devices have been prepared by a procedure that involves phase separation of nematic liquid crystal from a homogeneous solution of liquid crystal and synthetic resin to form a liquid crystal phase interspersed with a polymer phase. Some advantages of these films are discussed in U.S. Pat. Nos. 4,671,618; 4,673,255; 4,685,771; 4,688,900 and 4,890,902, the disclosures of which are incorporated herein by reference.
A further development of liquid crystal-polymer films disclosed in U.S. Pat. No. 4,994,204, involves the use of a birefringent polymer, e.g., a liquid crystal polymer. The films prepared with birefringent polymer have the characteristic of displaying haze-free transparency for all directions of incident light. This is accomplished by matching the ordinary and extraordinary indices of refraction of the polymer to the ordinary and extraordinary indices of refraction of the liquid crystal. Films made with birefringent polymer can operate in a normal manner so that they are clear in the field-ON state and light scattering in a field-OFF state or, alternatively, can operate in a reverse or "fail-safe" mode where the material is clear in the absence of a field and is light scattering in the field-ON state.
In each case, the prior liquid crystal-polymer films are prepared by introducing the solution of liquid crystal and polymerizable material between two substrates. The substrates, which are typically glass or plastic sheets, are spaced apart and sealed around the edges. Once the liquid crystal material is disposed between the substrates, the composition is polymerized to form a thin film. The inner surfaces of the substrates are typically treated with, for example, rubbed polyamide layers or other chemicals to induce surface alignment of the liquid crystal molecules parallel to the cell walls. Transparent electrodes are typically coated onto the substrates to switch the material in the thin film between electrooptical conditions.